LEXUS SC400 1991 Service Repair Manual

37. DISCONNECT ENGINE WIRE FROM LH CYLINDER HEAD
Remove the five bolts, and disconnect the engine wire.
38. REMOVE ENGINE HANGERS Remove the two bolts and engine hanger. Remove the two
engine hangers.
39. REMOVE CYLINDER HEAD COVERS Remove the eight bolts, seal washers, cylinder head cover
and gasket. Remove the two cylinder head covers.
40. IF NECESSARY, REMOVE SEMI±CIRCULAR PLUGS
41. REMOVE CAMSHAFTS NOTICE: Since the thrust clearance of the camshaft is
small, the camshaft must be held level while it is being
removed. If the camshaft is not kept level, the portion of
the cylinder head receiving the shaft thrust may crack or
be damaged, causing due the camshaft to seize or break.
To avoid this, the following steps should be carried out.
A. Remove exhaust camshaft from RH cylinder head
(a) Bring the service bolt hole of the driven s ub±gear
upward by turning the hexagon wrench head portion of
the exhaust camshaft with a wrench.
(b) Secure the exhaust camshaft sub±gear to the driven
gear with a service bolt.
Recommended service bolt: Thread diameter 6 mm
Thread pitch 1.0 mm
Bolt length 16±20 mm (0.63±0.79 in.)
HINT: When removing the camshaft, make certain that the
torsional spring force of the sub±gear has been eliminated by
the above operation.
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(c) Set the timing mark (one dot mark) of the camshaftdriven gear at approx. 105 angle by turning the hexagon
wrench head portion of the exhaust camshaft with a
wrench.
(d) Alternately loosen and remove the two bearing cap bolts
holding the intake camshaft side of the oil feed pipe to
the cylinder head.
(e) Uniformly loosen and remove the eight bearing cap bolts in several passes in the sequence shown.
(f) Re mo ve th e oil fe e d pip e , fo u r be a rin g ca p s an d
exhaust camshaft.
B. Remove intake camshaft from RH cylinder head (a) Remove the rear bearing cap.
(b) Set the timing mark ( one dot mark) of the camshaft drive
gear at approx. 455 angle by turning the hexagon
wrench head portion of the intake camshaft with a
wrench.
(c) Uniformly loosen and remove the eight bearing cap bolts in several passes in the sequence shown.
(d) Remove the four bearing caps, oil seal and intake
camshaft.
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C. Remove exhaust camshaft from LH cylinder head(a) Bring the service bolt hole of the driven s ub±gear
upward by turning the hexagon wrench head portion of
the exhaust camshaft with a wrench.
(b) Secure the exhaust camshaft sub±gear to the driven gear with a service bolt.
Recommended service bolt: Thread diameter 6 mm
Thread pitch 1.0 mm
Bolt length 16±20 mm (0.63±0.79 in.)
HINT: When removing the camshaft, make certain that the
torsional spring force of the sub±gear has been eliminated by
the above operation.
(c) Set the timing mark (two dot marks) of the camshaft
driven gear at approx. 155 angle by turning the hexagon
wrench head portion of the exhaust camshaft with a
wrench.
(d) Alternately loosen and remove the two bearing cap bolts
holding the intake camshaft side of the oil feed pipe to
the cylinder head.
(e) Uniformly loosen and remove the eight bearing cap bolts in several passes in the sequence shown.
(f) Re mo ve th e oil fe e d pip e , fo u r be a rin g ca p s an d
exhaust camshaft.
D. Remove intake camshaft from LH cylinder head (a) Remove the front bearing cap.
(b) Set the timing mark ( one dot mark) of the camshaft drive
gear at approx. 605 angle by turning the hexagon
wrench head portion of the intake camshaft with a
wrench.
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(c) Uniformly loosen and remove the eight bearing capbolts in several passes in the sequence shown.
(d) Remove the four bearing caps, oil seal and intake camshaft.
HINT: Arrange the bearing caps in correct order.
42. DISASSEMBLE EXHAUST CAMSHAFTS (a) M ount the hexagon wrench head portion of the
camshaft in a vise.
NOTICE: Be careful not to damage the camshaft.
(b) Insert a service bolt (A) into the service hole of the camshaft sub±gear.
(c) Using a screwdriver, turn the sub±gear clockwise, and
remove the service bolt (B).
NOTICE: Be careful not to damage the camshaft.
(d) Using snap ring pliers, remove the snap ring.
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(e) Remove the following parts:(1) Wave washer
(2) Camshaft sub±gear
(3) Camshaft gear spring
HINT: Arrange the camshaft sub±gears and gear springs (RH
side and LH side).
43. REMOVE CIRCULAR PLUGS Remove the two bolts, seal washers, bearing cap and circular
plug. Remove the two circular plugs.
HINT: Arrange the bearing caps (RH side and LH side).
44. DISCONNECT MAIN OXYGEN SENSOR CONNECTORS Disconnect the RH and LH oxygen sensor connector.
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45. REMOVE CYLINDER HEADS(a) Uniformly loosen the ten cylinder head bolts on one side
of each cylinder head in several passes in the sequence
shown, then do the other side as shown. Remove the
twenty cylinder head bolts and plate washers.
NOTICE: Head warpage or cracking could result from re-
moving bolts in an incorrect order.
(b) Lift the cylinder heads from the dowels on the cylinder block, and place the two cylinder heads on wooden
blocks on a bench.
HINT: If the cylinder head is difficult to lift off, pry between the
cylinder head and cylinder block with a screwdriver.
NOTICE: Be careful not to damage the contact surfaces
of the cylinder head and cylinder block.
46. REMOVE EXHAUST MANIFOLD FROM RH CYLINDER HEAD
(a) Remove the three bolts and heat insulator.
(b) Remove the main oxygen sensor.
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(c) Remove the eight nuts, exhaust manifold and gasket.
47. REMOVE EXHAUST MANIFOLD FROM LH CYLINDER HEAD
(a) Remove the three bolts and heat insulator.
(b) Remove the main oxygen sensor.
(c) Remove the eight nuts, exhaust manifold and gasket.
DISASSEMBLY OF CYLINDER HEADS
(See Components on page EM±59)
1. REMOVE VALVE LIFTERS AND ADJUSTING SHIMS
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HINT: Arrange the valve lifters and adjusting shims in correct
order.
2. REMOVE VALVES (a) Using SST, compress the valve spring and remove thetwo keepers.
SST 09202±70010
(b) Remove the following parts: (1) Spring retainer
(2) Valve spring
(3) Valve
(4) Spring seat
HINT: Arrange the valves, valve springs, spring seats and
spring retainers in correct order.
(c) Using needle±nose pliers, remove the oil seal.
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INSPECTION, CLEANING AND REPAIR
OF CYLINDER HEAD COMPONENTS
1. CLEAN TOP SURFACES OF PISTONS AND CYLINDERBLOCK
(a) Turn the crankshaft and bring each piston to top deadcenter (TDC). Using a gasket scraper, remove all the
carbon from the piston top surfaces.
(b) Using a gasket scraper, remove all the gasket material from the top surfaces of the cylinder block.
(c) Using compressed air, blow carbon and oil from the bolt
holes.
CAUTION: Protect your eyes when using high±pressure
compressed air.
2. CLEAN CYLINDER HEADS
A. Remove gasket material Using a gasket scraper, remove all the gasket material from the cylinder block surface.
NOTICE: Be careful not to scratch the cylinder block con-
tact surface.
B. Clean combustion chambers Using a wire brush, remove all the carbon from the combus-
tion chambers.
NOTICE: Be careful not to scratch the cylinder block con-
tact surface.
C. Clean valve guide bushings Using a valve guide bushing brush and solvent, clean all the
guide bushings.
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D. Clean cylinder headsUsing a soft brush and solvent, thoroughly clean the cylinder
heads.
3. INSPECT CYLINDER HEADS
A. Inspect for flatness Using a precision straight edge and feeler gauge, measure
the surfaces contacting the cylinder block and manifolds for
warpage.
Maximum warpage: 0.10 mm (0.0039 in.)
If warpage is greater than maximum, replace the cylinder
head.
B. Inspect for cracks Using a dye penetrant, check the combustion chamber, in-
take ports, exhaust ports and cylinder block surface for
cracks.
If cracked, replace the cylinder head.
4. CLEAN VALVES (a) Using a gasket scraper, chip any carbon from the valvehead.
(b) Using a wire brush, thoroughly clean the valve.
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